The use of various ferrites in a steam cracker to produce olefins from paraffins is known. Introducing ferrites such as zinc, cadmium, and manganese ferrites (i.e., mixed oxides with iron oxide) into a dehydrogenation zone at a temperature from about 250° C. up to about 750° C. at pressures less than 100 psi (689.476 kPa) for a time less than 2 seconds, typically from 0.005 to 0.9 seconds are also known. These reactions appear to take place in the presence of steam that may tend to shift the equilibrium in the “wrong” direction. Additionally, the reaction does not take place in the presence of a catalyst.
In addition, it is known that nickel ferrite may be used in the oxidative dehydrogenation process using reaction conditions comparable to those noted above.
In some Petro-Tex patents, the metal ferrite (e.g., M FeO4 where, for example, M is Mg, Mn, Co, Ni, Zn or Cd) is circulated through the dehydrogenation zone and then to a regeneration zone where the ferrite is re-oxidized and then fed back to the dehydrogenation zone.
It is interesting to note that the ferrite reversible takes up and releases oxygen.
Also known is a catalyst for the oxidative dehydrogenation of a paraffin (alkane) such as ethane. The gaseous feedstock comprises at least the alkane and oxygen, but may also include diluents (such as, argon, nitrogen, etc.) or other components (such as, water or carbon dioxide). The dehydrogenation catalyst comprises at least about 2 weight % of NiO and a broad range of other elements preferably Nb, Ta, and Co. While NiO is present in the catalyst, it does not appear to be the source of the oxygen for the oxidative dehydrogenation of the alkane (ethane).
Also known are sol gel supported catalysts for the oxidative dehydrogenation of ethane to ethylene. The catalyst appears to be a mixed metal system, such as, Ni—Co—Mo, V—Nb—Mo possibly doped with small amounts of Li, Na, K, Rb, and Cs on a mixed silica oxide/titanium oxide support. Again, the catalyst does not provide the oxygen for the oxidative dehydrogenation, rather gaseous oxygen is included in the feed.
Also known is a catalyst of the composition LiO—TiO2, which is characterized by a low ethane conversion not exceeding 10%, in spite of a rather high selectivity to ethylene (92%). The catalyst is used in a high temperature process of oxidative dehydrogenation, which is close to or higher than 650° C.
The preparation of a supported catalyst usable for low temperature oxy-dehydrogenation of ethane to ethylene has been disclosed. A supported catalyst for the low temperature gas phase oxydehydrogenation of ethane to ethylene is prepared by (a) preparing a precursor solution having soluble and insoluble portions of metal compounds; (b) separating the soluble portion; (c) impregnating a catalyst support with the soluble portion and (d) activating the impregnated support to obtain the catalyst. The calcined catalyst has the composition MoaVbNbcSbdXe. X is nothing or Li, Sc, Na, Be, Mg, Ca, Sr, Ba, Ti, Zr, Hf, Y, Ta, Cr, Fe, Co, Ni, Ce, La, Zn, Cd, Hg, Al, Tl, Pb, As, Bi, Te, U, Mn and/or W; a is 0.5 to 0.9, b is 0.1 to 0.4, c is 0.001 to 0.2, d is 0.001 to 0.1, e is 0.001 to 0.1 when X is present.
Another example of the low temperature oxy-dehydrogenation of ethane to ethylene using a calcined oxide catalyst containing molybdenum, vanadium, niobium and antimony is the calcined catalyst containing MoaVbNbcSbdXe in the form of oxides. The catalyst is prepared from a solution of soluble compounds and/or complexes and/or compounds of each of the metals. The dried catalyst is calcined by heating at 220 to 550° C. in air or oxygen. The catalyst precursor solutions may be supported on to a support, e.g., silica, aluminum oxide, silicon carbide, zirconia, titania or mixtures of these. The selectivity to ethylene may be greater than 65% for a 50% conversion of ethane.
Also disclosed elsewhere are Pt—Sn—Sb—Cu—Ag monolith systems that have been tested in an auto-thermal regime at T>750° C., the starting gas mixture contained hydrogen (H2:O2=2:1, GHSV=80,000 h−1). The catalyst composition is different from that of the present disclosure and does not contemplate the use of molecular hydrogen in the feed.
Also disclosed elsewhere are mixed metal oxide catalysts of V—Mo—Nb—Sb. At 375 to 400° C., the ethane conversion reached 70% with the selectivity close to 71 to 73%. However, these parameters were achieved only at very low gas hourly space velocities less than 900 h−1 (i.e., 720 h−1).
Japanese Patent 07053414 teaches a silica supported catalyst of the formula Mo1.V0.3Nb0.12Te0.23On where n satisfies the valence of the catalyst for the dehydrogenation of ethane.
Also disclosed elsewhere are Mo—V—Te—Nb—O oxide catalysts that provide an ethane conversion of 50 to 70% and selectivity to ethylene up to 95% (at 38% conversion) at 360 to 400° C. The catalysts have the empirical formula MoTehViNbjAkOx, where A is a fifth modifying element. The catalyst is a calcined mixed oxide (at least of Mo, Te, V and Nb), optionally supported on: (i) silica, alumina and/or titania, preferably silica at 20 to 70 wt % of the total supported catalyst or (ii) silicon carbide. The supported catalyst is prepared by conventional methods of precipitation from solutions, drying the precipitate then calcining.
A known preparation of a Mo—Te—V—Nb composition involves preparing a slurry by combining an inert ceramic carrier with at least one solution comprising ionic species of Mo, V, Te, and Nb, drying the slurry to obtain a particulate product, pre-calcining the dried product at 150 to 350° C. in an oxygen containing atmosphere and calcining the dried product at 350 to 750° C. under inert atmosphere. The catalyst prepared exhibits the activity and selectivity in the oxidation reaction comparable to the non-supported catalyst.
A process for preparation of ethylene from gaseous feed comprising ethane and oxygen involving contacting the feed with a mixed oxide catalyst containing vanadium, molybdenum, tantalum and tellurium in a reactor to form effluent of ethylene has been disclosed. The catalyst has a selectivity for ethylene of 50 to 80%, thereby allowing oxidation of ethane to produce ethylene and acetic acid with high selectivity. The catalyst has the formula Mo1N0.3Ta0.1Te0.3Oz. The catalyst is optionally supported on a support selected from porous silicon dioxide, ignited silicon dioxide, kieselguhr, silica gel, porous and nonporous aluminum oxide, titanium dioxide, zirconium dioxide, thorium dioxide, lanthanum oxide, magnesium oxide, calcium oxide, barium oxide, tin oxide, cerium dioxide, zinc oxide, boron oxide, boron nitride, boron carbide, boron phosphate, zirconium phosphate, aluminum silicate, silicon nitride, silicon carbide, and glass, carbon, carbon-fiber, activated carbon, metal-oxide or metal networks and corresponding monoliths; or is encapsulated in a material (preferably silicon dioxide (SiO2), phosphorus pentoxide (P2O5), magnesium oxide (MgO), chromium trioxide (Cr2O3), titanium oxide (TiO2), zirconium oxide (ZrO2) or alumina (Al2O3). However, the methods of preparation of the supported compositions involve the procedures of wet chemistry (solutions are impregnated into the solid support and then the materials are dried and calcined).
A ceramic tube for use in the conventional dehydrogenation of ethane to ethylene. The “tube” is a ceramic membrane. The ethane flows inside the tube and hydrogen diffuses out of the tube to improve the reaction kinetics. The reactive ceramic is 5 microns thick on a 1.5 to 2 mm thick support.
SABIC teaches a process in which ceramic pellets are packed around a tubular reactor and different reactants flow around the outside and inside of the tube for use in the oxidative dehydrogenation of ethane to ethylene.
A zoned or layered oxidative reactor in which following a zone for oxidative dehydrogenation there is an “oxidation zone” following a dehydrogenation zone to oxidize the hydrogen to water is known. Following the oxidation zone, there is an adsorption bed to remove water from the reactants before they enter a subsequent dehydrogenation zone. This is to reduce the impact of water on downstream dehydrogenation catalysts.
Methods to remove residual oxygen from the product stream have been disclosed. A combustible, such as hydrogen or a hydrocarbon, may be added to the product stream to eliminate residual oxygen. The disclosure refers to a catalyst but does not disclose its composition. As noted above, it may then be necessary to treat the product stream to eliminate water.
Also known are processes for the partial catalytic oxidation of a hydrocarbon to a final product, such as, propene to acrolein or acrylic acid. The process appears to operate outside the explosive limits of propylene (Col. 32-33). Additionally, the final product stream contains small amounts of oxygen (1.5 to 3.5 vol. %, Col. 37, line 10). The residual oxygen content in the final product (acrylic acid) does not appear to be a concern for the inventors. In these processes, the catalyst is not regenerated in situ, it is replaced with new catalyst.
Other disclosures teach a coupling process for lower hydrocarbons to produce higher hydrocarbons involving halogenation (bromination) followed by an oxidative removal of halogen and coupling of the intermediate compounds to produce the final product. This is of interest as it teaches a forward, reverse feed to burn coke off one of the catalysts used in the process. This disclosure teaches away for recycling product through a reaction zone to eliminate residual oxygen.
It has been known to remove residual oxygen from the product stream of an oxidative dehydrogenation process by consuming the oxygen by burning hydrocarbons or hydrogen. This is expensive and reduces yields of and selectivity for the desired hydrocarbon.
Disclosed herein are simple ways to reduce the oxygen content in the product stream from an oxidative dehydrogenation reaction by passing the stream over a catalyst bed, to extract oxygen from the product stream and at least partially provide a source of oxygen for the catalyst.